The invention is based on a method and an arrangement for the temperature compensating at circular resonators with dual mode utilization for microwave filters realizable therefrom.
Circular resonators, which are used in operating environments in which the temperature fluctuates greatly, are equipped with various means for compensating for the thermal expansion caused by temperature fluctuations. A frequently employed principle for counteracting these thermal expansions consists of changing the volume of the circular resonators as a function of the temperature with the help of mechanical means in such a manner, that the transfer properties of the circular resonator are retained. Usually, devices are used for this purpose, which protrude into the interior of the circular resonator (DE 39 35 785) and change their volume there as a function of the temperature, so that the average frequency of the resonator remains constant. A further possibility consists of utilizing the effect of the resonator end faces (EP 0 939 450 A1, WO 87/03745). Compensating elements, which dip more or less into the interior of the resonator, can be adjusted only with difficulty and, because of the nonlinear field distortion, lead to a nonlinear frequency compensation.
In EP 0 939 450 A1, a circular resonator is closed off by an arrangement at the end face, which consists of two plates with different coefficients of thermal expansion, lying rigidly on top of one another. In WO 87/03745, a curved, thin copper plate protrudes at the end face into the interior of the circular resonator. For certain cases of application, for example, if, because of special quality requirements, so-called TE1 1n modes, with n>1, are used as working modes in circular resonators, the effect of end-side compensation becomes constantly less because of the unfavorable relationships between length and diameter. Especially at high frequencies (Ku, Ka or higher) this technique fails, since the necessary deformation of the end-side diaphragms no longer is sufficient. high frequencies (Ku, Ka or higher) this technique fails, since the necessary deformation of the end-side diaphragms no longer is sufficient.
An arrangement, for which the waveguide is clamped in at least one frame, the temperature-dependent expansion of which is less than that of the waveguide, can compensate for large temperature-dependent volume changes (DE 43 19 886). Moreover, at least at two mutually opposite places of its wall, the waveguide is connected non-positively with the frame. The frame and waveguide are connected non-positively over spacers, which transfer compression and tensile forces, resulting from the different thermal expansions of the frame and the waveguide, onto the waveguide wall and cause elastic deformations there. The end faces of the waveguide produce the bulk of the elastic deformation. Moreover, deformation forces may be transferred over spacers, disposed between the frame and the casing of the waveguide, also onto the frame and counteract undesirable buckling of the frame. The disadvantage of this solution consists therein that, at two opposite side walls, ribs are integrally molded as spacers to the spacers of the frame, that is, that the waveguide of the arrangement must be adapted for the temperature compensation, which is associated with additional expense.